By Sinéad O’Ferrall (@SineadOFGH)
Diseases can often be stomach turning, but for most people nothing has more “ick” factor than parasitic infections . Yet this does not diminish the seriousness of these diseases and the burden they place on the most vulnerable people in the poorest countries. Malaria, perhaps the most well known parasitic disease, is one of the leading causes of death and morbidity in developing countries.
Parasitic diseases cover a wide range of disease presentations, from the well-known ones such as malaria or ringworm to the more obscure ones like onchocerciasis (also known as river blindness or Robles Disease). So what links all these varying diseases? What distinguishes a parasitic disease from any other disease?
Well, a parasite is an organism that must inhabit another host to survive, at the expense of the host. It can be a temporary host to support one life stage of the parasite such as in the case of schistosomiasis, or it can be for the full life cycle of the parasite as seen with hookworm. If an organism infects your body and causes illness or lowers your quality of health, then it is a parasitic disease.
Another example of a parasitic disease, one that has been in the press recently, for all the right reasons, is the guinea worm (aka dracunculiasis). It may surprise you (or not) to discover that in all of recorded human history we have only ever gotten rid of one disease in its entirety – smallpox. The goal of so many scientists and health officials is to repeat the same again with lots of other diseases, with a focus on vaccines being the magic key to achieve this.
But there are many obstacles to creating vaccines, making it a timely process, so we cannot wait around to create a vaccine for every disease. Although vaccinations have proven successful in many cases, not every disease is suitable for vaccination, and guinea worm is an example of this. Thankfully, in this instance, we did not wait for a vaccine against the guinea worm.
A guinea worm infection is rarely fatal, but it is pretty horrific nevertheless. People typically catch it from drinking stagnant water that is infected with the larvae of the worm. The sandflies in the stagnant water ingest the worm’s eggs. They are then swallowed by a thirsty human and reach the stomach, where the worm’s larvae are released from the sandfly and enter our system through the intestinal wall. Once in our system, the worm larvae mate and females grow in the abdomen. They can grow up to a meter long and incubate for up to a year before creating a painful lesion on the skin which they emerge slowly through. This is an agonisingly painful process for the host i.e. a human.The cycle is perpetuated when the human places the painful lesion in water to relieve the burning sensation, and the eggs are released into the water to await a new host.
But if people don’t die from this disease, why has so much effort gone into eradicating it compared to some of the more fatal infections, such as malaria? It can be explained by two reasons:
- Though not fatal, it has a hugely negative impact on people’s lives.
- The guinea worm has what is known as a fragile transmission cycle, making it vulnerable to eradication.
“Guinea worm is a particularly devastating disease that incapacitates people for extended periods of time, making them unable to care for themselves, work, grow food for their families, or attend school.” Cartercentre.org
This quote is the reason the “Carter Centre” has dedicated huge resources and time to eradicating guinea worm disease, and why so many partners, such as health ministries, have joined them in their endeavours. The impact the disease has on people and communities is significant and damaging.
As for the second reason, guinea worm will likely soon be eradicated simply because it is relatively easy to do. Unlike malaria or schistosomiasis, which have complicated life cycles and extremely good survival tactics, the guinea worm is a survivor by chance and human-based habits. The transmission cycle is fragile making the guinea worm vulnerable. The cycle is dependent on humans introducing the eggs from the worm into the water by bathing the open wound and then using the same water to drink so we can ingest the infected sandfly. Poor water control and sanitation is the only reason infection still occurs. By changing our habits in relation to water, we can effectively wipe out guinea worm infections as has happened in so many countries so far. So through behavioural changes and improved infrastructure and water management, we are realistically looking at the end of the guinea worm infections.
The success of this non-vaccine strategy can be demonstrated by looking at the figures. In 1986 3.5 million people a year were infected with guinea worm in 21 countries throughout Asia and Africa. In 2014 only 126 cases were recorded in 4 countries – Chad (13 cases), South Sudan (70 cases), Mali (40 cases) and Ethiopia (3 cases). This is why talk has moved away from treatment and control, to elimination and eradication. It is a remarkable feat no matter which way you look at it.
Among other examples this intervention sets, it shows the importance of a cross-disciplinary approach to fighting disease. Scientists studied the disease, discovered the transmission route, and defined its cycle. But it was engineers, public health officers, education officers and water sanitation experts that came up with the solutions, and it was policy and political support that implemented the solutions and kept up the momentum needed to achieve this level of success. And it will be crucial now for the momentum to be upheld until we have completely gotten rid of the last few cases without creating any new ones.
The only question is, once we eliminate the guinea worm, what disease will be next? What an exciting question full of possibility that has not been felt since vaccination and the eradication of smallpox. Whether or not the success can be repeated, it makes this achievement and goal no less noble and admirable, and I’m sure it will be the global health accomplishment to beat for the years to come.